their online persona is separate from what I'm describing - in the DOJ release they post what looks like a picture from what they claim is Samourai marketing for investors that their revenue for their add-on would come from 'online gamblers, dark/greymarket participants, high net worth individuals, and asset protection/capital flight'

The stated or heavily implied intent of your product matters to the government in its ability to pursue charges against you. Explicitly stating that you want to raise money from investors to hide darkmarket money / people under sanction puts a target on your back.

I think that coinjoins are ok, actually. If they could be conducted in a way that didn't require a central coordinator that'd probably be alright.

However, if you decide to run a business whose sole purpose is to help users do coinjoins and you collect revenue from it, while advertising it as a way to facilitate crime, I expect the State to eventually come on the offense.

If Samourai didn't have that marketing material for investors, and did not collect fees + used some decentralized coordination, the feds would find it much more difficult to prosecute.